1. Field of the Invention
The present invention relates to a vibration measurement method and apparatus and in particular, to a vibration measurement method and apparatus capable of detecting a very small displacement, speed, and periodicity.
This vibration measurement method and apparatus can be applied to an experiment analysis such as an automobile production technology. More specifically, engine vibration analysis, body transmission and vibration analysis, analysis of noise in the cabin, and muffler vibration analysis. The present invention can also be applied to various other fields. Since the present invention can accurately measure a very small vibration with a non-contact state, it can be applied to an instrument damage such as a drill. Furthermore, the present invention can be applied to vibration of a plant using a motor, leak of a water pipe and a gas pipe. Furthermore, sweetness of a large size fruit such as watermelon can be checked according to the vibration caused by knocking. Here, the vibrating object to be measured includes a vast area from the engine to the watermelon.
2. Description of the Related Art
Conventionally, when measuring a vibration of an object to be measured, firstly, a laser beam oscillated from a laser resonator is applied through a lens to the surface of the vibrating object. The beam is scattered on the surface and a part of the scattered beam returns to the resonator and mixed with the oscillated beam, so that the Doppler speed component becomes a beat wave. By analyzing this beat wave, vibration periodicity, speed change, and displacement are calculated.
However, in the aforementioned conventional example, when a vibrating plane has displaced by half of the laser oscillation wavelength .lambda., a chopping wave is generated. Accordingly, it is difficult to measure a displacement smaller than .lambda./2 and the speed change.
Furthermore, in the conventional example, there is a problem that when the vibrating object displaces by a very small displacement, it is impossible to calculate vibration by replacing the Doppler frequency with a vibration plane moving speed.